1. Field of the Invention
The present invention relates to a technology of searching a point of interest (POI) set as a destination or the like in a navigation apparatus.
2. Description of the Related Art
A POI search function of searching a POI suited to preference or purpose of a user is of importance in a POI search for a navigation apparatus for automobile use, a communication terminal, and the like. Since a set of POI data subjected to a POI search is ever-changing as a matter of course, update of an obsolete POI data is required. If the update is made by rewriting only a changed portion of the POI data, a size of the POI data can be reduced, thus allowing distribution cost of the POI data also to be reduced.
Actually, however, a set of POI data includes not only a data of each POI but also a management data for managing the set of POI data as a whole and performing a search or an update thereof. The management data includes storage address values of respective POI data, of which data amount is enormous. Thus, even if a portion of a single POI data is rewritten, all the addresses that follow the rewritten POI data are displaced subsequently, and thus, a large volume of the displaced storage address values in the management data has to be rewritten.
For the reason described above, there is a problem that an update processing of POI data including the management data takes a large load. Japanese Published Patent Application No. 2005-043966 discloses a technique for solving the problem, in which a POI data which is stored at the time of manufacturing a device having a POI search function is managed separately from a POI data which is updated after the manufacturing. Further, the updated POI data is managed separately divided into a deleted POI data, an added POI data, and a changed POI data. A search result after the update is obtained by combining the POI data at the manufacturing with the deleted, added and changed POI data.
In some cases, however, a POI search according to the related art has a difficulty in quickly computing the number of found POIs, that is, the number of hits. More specifically, if a POI data stored at the time of manufacturing is managed separately from a POI data updated after the manufacturing, it is necessary to compute the number of the deleted POI data from among the POI data stored at the manufacturing so as to precisely obtain the most updated number of hits. For this purpose, the deleted POI data needs to be identified, and each of the identified deleted POI data needs to be determined whether or not it is actually deleted from a search result. Thus, if the number of hits as the search result is large, the number of times for checking the deleted POI data is also large, which increases a time required for computing the number of hits.
It is to be noted that the number of hits is an important measure in estimating a car navigation apparatus which requires saving of a trouble of inputs by a user as much as possible. In conducting a POI search, a user successively inputs search keywords so as to narrow search results. Desirably, the number of hits is not zero but not too large to be difficult in looking at all of the hit POI data one by one by the user. Thus, the number of hits is a good measure for estimating whether or not a user has obtained an appropriate number of search results. A quick presentation of the number of hits is indispensable for convenience of a user each time the user inputs a search keyword.
The present invention has been made in an attempt to meet such needs of users and provides a device and method for quickly obtaining the number of hits as a search result while reducing a load of processing.
In the present invention, the number of hits as a search result is calculated as follows. First, it is determined whether or not computation of the number of deleted POI data, which has already been deleted and is not a target of the search anymore, is to be reflected in computing the number of hits of the searched POI data. Only if the computation of the deleted number is determined to be reflected, the number of hits is computed by doing so. If not, without doing so.